I think my regional dialect of Portuguese has got to have the most confusing expression for outsiders ever: our use of "capaz" which literally means "capable". We use it like this:
— are you going to the party tomorrow?
Here's the kicker: "capable" means "no"!
It makes people from other Brazilian states *very* confused
When you ask someone from my state what "capaz"/"capable" means, they tell you with a smile: "capaz que não"/"it's capable that no"
The person will invariably then say, somewhat puzzled: "oh, so it means 'possibly not', then??"
"No, it means 'definitely not'!"
It comes to mind now also that we also use it as a possible answer for obrigado/"thank you", say, if you do someone a favor, as a way of saying "nevermind, it was no hassle!"
And now I can't help but find this exchange hilarious:
— thank you!